1. Field of the Invention
The present invention relates to a wireless terminal device, a gateway device, and a wireless data transfer control method. In particular, it relates to technology in a data communication system which executes an upper application such as an AV (audio/video) protocol as to a wireless network exhibiting dynamic variations in the condition of the wireless link or in an integrated network system encompassing a wireless network and wired network so as to perform efficient transfer of content data.
2. Related Art
With the recent increase in the use of digital equipment, the implementation of networks in the home has gained attention. At present, the IEEE Std 1394 (hereinafter abbreviated IEEE 1394), which was devised as a connecting wired for connection between AV equipment, has gained attention as a home-use network media. The IEEE 1394 is a high-speed bus capable of connection between a plurality of terminals by a daisy chain or star-configured connection, with transfer of broad bank data performed at speeds exceeding 100 Mbps. It is possible on a single wired to perform transfer both asynchronous data and isochronous data.
The achievement of high speeds in wireless networks (wireless LANs) is also gaining attention, and wireless LAN products conforming to IEEE Std 802.11 have already appeared and are going through a process of price reduction. Along with advancing speeds and price reductions for such wireless technology, there are active efforts being made to apply this wireless technology in the home network as well. In the US, such industry groups as Home RF and Bluetooth have been established, and great advances are expected in the future.
A high-speed, low-cost wireless network is thought to be highly acceptable for use in the home network. For this reason, a system that combines a high-speed, low-cost wireless LAN and the IEEE 1394 is expected to form the core of home networks in the future.
However, in an environment in which the IEEE 1394 bus is integrated with a wireless LAN, there are a number of problems.
The first problem is that protocols executed on the IEEE 1394 bus (for example, the AV/C Digital Interface Command Set General Specification, IEEE 1394-1995), were originally developed with the assumption of execution on a wired medium, and did not envision execution in a wireless environment. However, in contrast to a wired network, it is known that there are changes related to the condition of the wireless link (for example, the bandwidth that can be used for transmission). To accommodate such wireless link condition changes, a method (such as fallback) is employed, wherein the wireless transfer speed (or type of modulation to be used) is established, for example, when the wireless LAN is started up, so as to start data communication at transfer speed suited to the wireless link condition. For this reason, when executing an upper layer protocol such as AV/C in a wireless environment, unless the condition of the lower layers is known, a problem can be envisioned such as when a request is made of a lower layer for transfer of content data (such as AV (audiovisual) data) which in reality cannot be transferred.
In current wireless LAN specifications (such as Bluetooth), however, there are no functions for “acquiring condition information of the wireless link” or “notify an upper application of the condition of the wireless link.” Additionally, because upper applications on the IEEE 1394 (such as the AV/C Protocol) were devised with the assumption of execution in a wired network, these upper applications also lack an “information element for holding link condition information” and a function for “acquiring link condition information.”
In the case in which AV data is transferred on a medium in which the link condition (such as usable transmission bandwidth) varies, such as in a wireless network, when an upper layer protocol (upper application) such as AV/C is executed, it was not possible to ascertain the condition of the link, which represents a downstream layer. For this reason, it was difficult to select the AV data type and transfer rate usable on the linked to be used and to perform smooth, efficient AV data transfer.